This invention relates generally to mechanical devices for converting an input having a substantially constant angular velocity to an output having a different angular velocity. More particularly, the present invention concerns an infinitely variable transmission in which the output angular velocity is continuously adjustable from a maximum positive value, through the zero output value, and to a maximum negative value.
Speed changing devices are employed in many types of equipment. In a simple transmission, for example, devices are often provided to give one or more discrete output speeds in relation to an input speed. In other equipment, it is necessary to have a wider variety of output speeds available. In such other equipment, the output speed often needs to vary continuously, or infinitely, over the desired speed range while only a constant speed is available as the input. For purposes of this specification, a "simple transmission" is a transmission having one or more discrete output speeds in relation to the input speed--and may include a discrete reverse (or negative) output speed. A "continuously viable transmission" is a transmission in which the ratio of output angular velocity to input angular velocity can be varied continuously from a first value to a second value--both having the same algebraic sign. A "continuously variable transmission" may also include a discrete reverse gear--having an algebraic sign different from the first and second values. An "infinitely variable transmission" is a transmission in which the ratio of output angular velocity to input angular velocity can be varied continuously from a first value to a second value--where the first and second values have different algebraic signs. Thus, the "infinitely variable transmission includes the "infinite" condition where the ratio of the input angular velocity to the output angular velocity is undetermined, i.e., .infin..
One of the more common continuously variable speed changing devices employs a fixed length V-belt and a pair of cooperating pulleys. The pulleys may have the ability to adjust the V diameter on which the belt operates in order to obtain a variable output speed. Typically, one such adjustable pulley mechanism is driven while another adjustable pulley mechanism is spring-loaded to maintain tension on the V-belt and to make the second adjustable pulley mechanism responsive to changes made in the first driven adjustable pulley mechanism. It will be appreciated by those skilled in the art that there is a practical mechanical limit to such devices, e.g., where the V-belt cannot be wrapped around a very small diameter shaft.
A somewhat analogous speed changing device employs a variable V-drive in combination with another traction driven fixed-width drum. Sometimes a plurality of these drums are employed to increase the maximum power transmission capability. These devices occasionally use elements packaged in planetary movement arrangements with one device at the center and a multiplicity of encircling meshing elements having planetary movements.
Another class of variable speed drives can be characterized as the ball and disc type. In this class of drive mechanism, the rotational axis for a ball element is usually at a substantially right angle to the rotational axis of a disc element. The ball element which has a surface of revolution is positioned so that when it is pressed against the rotating disc element, the ball element is driven by the disc. By moving the ball element along a radius of the disc element, a variable speed drive can be obtained from the ball element.
Another class of speed regulation employs purely inertial devices. Flywheel governors are common examples of inertial devices that have been used to control internal combustion engine speed under varying load conditions for many years.
Each of the various infinitely adjustable speed changing devices currently available have various problems and limitations. One common problem is the presence of residual slippage between traction elements. Such slippage is undesirable since it wastes energy, generates heat, promotes wear, and increases working clearances.
Another common problem is that many of the materials commonly used to fabricate components of variable speed devices are subject to rapid wear. As a result, the devices experience increased clearances with attendant noise, slippage and reduced efficiency. Wear also tends to create objectionable dirt and particles resulting from degradation of the materials.
Many available speed changing devices also exhibit poor power transmission capability for the spatial volume which they occupy. That is, a large and usually heavy transmission is needed to transmit modest power levels. As a result, to transmit large amounts of power, a physically large transmission is required, adding to the weight of the device.
Many of the available speed changing devices also fail to provide the ability to reverse the direction of output rotation while the input operates at a uniform speed in a constant direction. This capacity can be desirable for example in motorized vehicles where a constant speed input could be varied so as to provide both forward and reverse drive speeds.
Most known transmission systems are also critically dependent upon lubrication, cleanliness or transmission fluids in order to provide and maintain their speed change capability. In many desirable applications of variable speed transmissions, it is extremely difficult, if not impossible, to lubricate or maintain cleanliness.
Another deficiency of most known speed change devices is the necessity for a clutch to permit the output speed or angular velocity to go to zero (i.e., stop) while the power supply is still operating. Clutches clearly introduce additional complexity into a system as well as expense, bulk, and weight. In a similar vein, most known devices which do permit a zero output speed lack sufficient traction at that speed to be useful. Traction near zero is necessary in order to create useful starting movement without slippage in the transmission device, and to produce braking through the internal deceleration of components.
Still further, most known devices are unable to run at the maximum speeds that could be advantageous for many applications. This inability to run at high speed is often a result of the fact that locally generated heat can devulcanize rubber, soften heat-treated materials, generate noise, and cause vibrations as well as other undesirable effects.
The control of known variable speed devices has also been a problem. More particularly, most devices do not have a sufficiently sensitive control that can produce small changes in the output speed settings. In many useful applications for variable speed devices, such sensitivity to small changes in response are highly desirable.
Conversion of an input angular velocity to a variable output angular velocity is, of course, the purpose of myriad transmission devices. With automotive transmissions, the input angular velocity is directly connected to the output so that the output angular velocity varies in direct relationship to the input angular velocity variation. In such transmissions, it is necessary to provide a clutch mechanism so that the output angular velocity can be zero while the input angular velocity is non-zero. Shifting between predetermined gear ratios simply changes the proportionality constant between the input and output angular velocities.
One known device for infinitely varying the speed of an output member while an input operates at a constant speed employs a reflexively curved endless metal band. Such a device is capable of generating both forward and reverse direction, including the zero output speed while the input continues to operate at a constant speed. See, U.S. Pat. No. 4,567,789, issued to D. F. Wilkes, on Feb. 4, 1986. Such a device, however, relies upon an endless metal band--which has not yet been reduced to actual practice.
Other transmissions are known in which planetary gear systems are used between an input and an output to effect speed differences. For example, in U.S. Pat. No. 1,149,816, issued to Fay on Aug. 10, 1915, an input shaft drives an auxiliary shaft by a meshed gear set. In addition, the input shaft drives a sun gear meshed with planetary gear sets carried by a second sun gear journaled to the output shaft. That second sun gear is driven by a pinion carried by the auxiliary shaft. Finally, the output shaft is driven by a third sun gear meshed with the planetary gear set. The Fay device, however, operates at a single speed. While other embodiments permit operation at different speeds, those different speeds are obtained by selective engagement of set screws. The Fay device is not arranged to generate different output speeds for a constant input speed.
The Blackwell patent (U.S. Pat. No. 1,445,741) illustrates a planetary gear set carried by a central wheel. A sun gear mounted on the input shaft meshes with the planetary gear set and is driven by a worm gear. That worm gear, in turn is driven from an auxiliary shaft that itself is driven by a gear carried by the output shaft. The output shaft is driven by a sun gear meshed with the planetary gear set. Here again, them is no mechanism for generating different output speeds for a constant input speed.
Other speed transmission devices are also known including, for example, U.S. Pat. No. 1,728,899 issued to Hegeler et al., U.S. Pat. No. 1,977,553 issued to Halford, and U.S. Pat. No. 5,033,995 issued to Salesse.
Various speed changing devices are also known which use variable pulley belt drives in association with geared systems. See for example, U.S. Re. Pat. No. 31,461 issued to Smirl, U.S. Pat. No. 5,121,936 issued to Cowan, U.S. Pat. No. 4,392,394 issued to Hofbauer et at., and U.S. Pat. No. 4,706,518 issued to Moroto et at. An epicylic transmission is also known which generates variable output speeds without using variable pulley belt drives. See for example, U.S. Pat. No. 5,360,380 issued to Nottle.